In many electronic systems and products, multiple printed circuit boards are used with connectors, harnesses and cables making circuit connections between them. Interconnection of circuit boards may be accomplished by the use of surface mount connectors, wires or wire cables, flex circuit strips, edge connectors, wire pins or shunts. Typically, these connections carry power from one circuit to another, as well as conductors for electronic communication, sensing and control. While there are many types of connections, there are limitations and disadvantages to most of them.
In some applications it is desirable to connect one board to another over a short distance, with minimal numbers of components and material employed in the connection. Further, the type and number of interconnections has a strong effect on reliability. Conventional cables and harnesses employ wires, terminals and pins, which must be joined together mechanically. Failure in any one of these joints or reduction in conductivity due to mechanical effects, corrosion or fracture will cause failure of the circuit. For this reason, solder joints are often used because of their reliability and permanence.
Solder connection between circuit boards, while being reliable, usually require the spanning of the distance between boards or conductors with a conductor—such as a pin (a shunt being a larger form of pin) or a wire. Pins are rigid and sometimes present unwanted stresses on the board and connection locations (the pads and holes). Secondary mechanical structures are added to reduce and control stresses. The pins themselves must be soldered to the board either manually (one at a time) or using special equipment. Press-in pins (pins, which rely on mechanical interference with conductors or pads) are sometimes used when geometries are fixed and well controlled.
Wires are flexible but are more difficult to reliably solder join and lack the structure for mechanical linkage when this is required. Typically, wires are directly soldered onto boards and are inserted through holes or soldered onto an enlarged copper pad. Direct soldering of wires is often done manually or with the use of equipment specialized for this purpose. Additional mechanical structures, called strain relief, are required to prevent mechanical fatigue and fraying of the wire adjacent to the solder joint if any type of motion or vibration is anticipated.
A third type of interconnect, called a flex circuit, is particularly advantageous where multiple circuits are joined carrying small amounts of current in limited space. Flex circuits are typically made by printing a thin metal conductive layer with a conductive pattern on a highly flexible plastic substrate. To prevent damage to the thin conductive layer, an additional layer of plastic is laminated over the conductor to form a sandwich. Access to the conductors is provided via holes in one or both of the plastic layers. Still, in order to gain robustness at the connecting ends, mechanical connectors or soldered pins must be added to the design. Flex circuits usually do not add to the mechanical stability or strength of the board-to-board connection.
For almost all of these connection methods described above, protection of the connection from shorting contact, mechanical damage or ESD discharge requires an additional mechanical cover or coating to be added after the solder connection, adding more complexity and cost to the implementation. Also, most of these interconnection methods present difficulties because of their mechanical sizes, geometries and lack of precise and flat mating surfaces for use on strictly surface mount boards.
In various applications, such as production of high power solid state (LED) lighting strips it is advantageous to have interconnections between circuit boards which are highly reliable, carry significant levels of current or voltage without loss, are protected from mechanical damage and shorting, allow various shapes and geometries of connection and are easy and efficient to apply. Embodiments of the present invention described below describe interconnections providing specific advantages over both traditional and more recent methods of interconnect such as the newly introduced FlexRAD system of continuous connection. Embodiments of the present invention include aspects addressing the strength, reliability and usability of interconnects between the semi-flexible substrates in order to produce long strips or continuous reels for ease in fixture assembly.
Long lengths and or continuous runs of SSL circuit strips are desirable for the reasons stated above. In addition the format of these semi-flexible continuous circuits is beneficial to the manufacture of the continuous circuit or installation into the final SSL fixture. Embodiments of the present invention described below conceive numerous methods to reduce manufacturing, installation and assembly costs. These system cost reductions further enable the adoption of SSL in a variety of applications thus reducing global energy consumption.
Solid-state lighting (SSL) refers to a type of lighting that utilizes light-emitting diodes (LEDs), organic light-emitting diodes (OLED), or polymer light-emitting diodes (PLED) as sources of illumination rather than electrical filaments, plasma (used in arc lamps such as fluorescent lamps), or gas. The term “solid state” refers to the fact light in an LED is emitted from a solid object; a block of semiconductor rather than from a vacuum or gas tube, as is the case in traditional incandescent light bulbs and fluorescent lamps. Compared to incandescent lighting, however, SSL creates visible light with reduced heat generation or parasitic energy dissipation, similar to fluorescent lighting. In addition, its solid-state nature provides for greater resistance to shock, vibration and wear, thereby increasing its lifespan significantly. Solid-state lighting is often used in traffic lights and is also used frequently in modern vehicle lights, train marker lights etc.